DE2840124B2 - Process for the production of butadiene from a C4 hydrocarbon mixture - Google Patents

Description

The present invention relates to a process for the production of butadiene from a butadiene and small amounts of styrene-containing green hydrocarbon mixture.

It is known. Butadiene from butadiene-containing Q-hydrocarbon mixtures by extractive distillation using a selective solvent. That from extractive distillation The butadiene obtained is generally then subjected to a conventional distillation.

An important use of the butadiene obtained by extractive distillation is its manufacture of butadiene-styrene copolymers, with a butadiene waste stream containing styrene after the polymerization is obtained. This waste stream can be incinerated, for example, but is convenient returned to a butadiene extraction plant. By initiating the polymerization with oxygen the butadiene waste stream containing styrene may still contain small amounts of oxygen.

Direct recycling of the butadiene waste stream containing small amounts of styrene and optionally oxygen in a butadiene extraction plant would become undesirable within the bitadiene extraction plant Lead to polymer formation. This would considerably reduce the running times of the system.

An advantageous process has now been found for obtaining butadiene with the aid of a selective solvent from a C ₁ hydrocarbon mixture which contains butadiene, small amounts of styrene and optionally oxygen, hydrocarbons more soluble in the selective solvent than butadiene and less soluble hydrocarbons than butadiene in the selective solvent , in which the Q hydrocarbon mixture is separated by extractive distillation into a distillate containing the less soluble hydrocarbons, a stream of butadiene and a stream containing the more soluble hydrocarbons, which is characterized in that the C4 hydrocarbon mixture is preceded by an extractive distillation Distillation zone, a mixture of styrene and Ci hydrocarbons is separated, the bottom temperature of the distillation zone being kept between 40 and 70 ⁰ C, and the top product of the distillation zone of the extractive D estillation is supplied.

According to the new process, it is possible to obtain butadiene from CV hydrocarbon mixtures without Having to drag styrene into the butadiene layer, so that the process can be carried out continuously becomes possible over extended periods of time.

In a preferred embodiment of the process, the upstream distillation zone is at the same time a second stream of liquid or gaseous C) and / or C4 hydrocarbons is supplied. By this procedure can be used with the separation of the mixture of styrene and C <hydrocarbons associated butadiene loss can be kept particularly low.

The starting C4-carbon mixture containing small amounts of styrene are used, for example, in the production of butadiene-siyrene copolymers

th received. In addition to butadiene and styrene, such mixtures can also contain 2-butene-cis, 2-butene-trans, butadiene-IA Butane, isobutane, butene-1, butyne-1, butenine and Cs hydrocarbons such as propane, propene, propadiene and propyne. In general, the starting Q hydrocarbon mixtures have styrene contents from 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

According to the invention containing from small amounts of styrene output Q-hydrocarbon mixture wherein the bottom temperature of the distillation zone between 40 and 70 ⁰ C is maintained is in one of the extractive distillation, a mixture of styrene and Q-hydrocarbons, suitably separated upstream distillation zone as a bottom product, is and the top product of the upstream distillation zone is fed to the extractive distillation. In general, the separated mixture of styrene and the Q-hydrocarbons has a styrene content of from 0.1 to 30% by weight, preferably from 1 to 20% by weight, in particular from 2 to 15% by weight, v; the upper limit on the styrene content generally results from the limit on the sump temperature. Surprisingly, the polymerization of styrene and butadiene can be kept small when a bottom temperature between 40 and 70 ⁰ C, preferably between 45 and 50 ⁰ C, is set in the upstream distillation zone.

On the other hand, it is advantageous to generate the reflux of the column by condensing the Q-hydrocarbons with cooling water. This results in a high content of Q hydrocarbons in the bottom product and thus a considerable loss of butadiene. In an advantageous embodiment of the invention, this ^{butadiene loss associated with the separation of the i r} , mixture of styrene and Q-hydrocarbons can be kept very low. The advantageous embodiment of the process according to the invention consists in that a second stream of liquid or gaseous C ₃ and / or Q hydrocarbons is fed to the upstream distillation zone at the same time.

Expediently, liquid or gaseous Cj and / or Q hydrocarbons with a lower butadiene _{content than the starting C 4} hydrocarbons are used, e.g. B. with less than 90% of the butadiene content of the starting Q-hydrocarbon mixture, preferably substantially butadiene-free hydrocarbons, e.g. B. with a butadiene content of less than 5 wt .-%, advantageously less than 1 wt .-%, pin set. It is advantageous to use saturated and / or mono- olefinically unsaturated Cj and / or Q hydrocarbons. Suitable hydrocarbons are e.g. B. propane, propene, butanes, η-butene, isobutene, 2-butenes, 1,2-butadiene or ^{mixtures containing these r} > ^r > hydrocarbons. Q-hydrocarbon mixtures are advantageously used. In a preferred embodiment of the process, the raffinate obtained in the extractive distillation is used, which contains the butanes and butenes mi.

In general, that of the upstream Second hydrocarbon stream to be fed to the distillation zone at or advantageously below the feed point of the >>> starting Q-hydrocarbon mixture of the upstream Supplied to the distillation zone, with a feed in the lower third, advantageously in the lower Quarter, in particular at the bottom of the upstream distillation zone, is preferred. Through the feeder of the second hydrocarbon stream below the feed point of the starting Q-hydrocarbon mixture a mixture of styrene becomes the bottom product as a result of the countercurrent washing that takes place and Q-hydrocarbons with a low butadiene content, z. B. less than 30 wt .-%, preferably less than 5 wt .-% butadiene, separated, so that by this method of operation with the styrene separation associated butadiene loss can be kept particularly low. In a preferred embodiment of the process of the present invention, the second hydrocarbon stream becomes that from the sump mixed with rising vapor of the upstream distillation zone or as a liquid in the sump fed.

The starting Q-hydrocarbon mixture to be used according to the invention styrene can also develop small amounts of oxygen. In this The starting Q hydrocarbon mixture containing small amounts of styrene and oxygen is used expediently first fed to a distillation zone for the separation of oxygen, in which the oxygen containing top product and a bottom product containing the styrene. That Styrene-containing bottom product is then used as a feedstock for extractive distillation upstream distillation zone used.

The distillation zone for the separation of oxygen can be provided with its own reboiler in order to to generate the steam required for the separation. In a preferred embodiment of the According to the method of the invention, part of the top product is that of the upstream extractive destination Distillation zone, generally 5 to 50%, preferably 10 to 20% of the top product, at the bottom fed to the distillation zone for the removal of oxygen, preferably as a gaseous stream.

Bride distillation zones can be structurally separated in two columns or structurally combined in one column be switched. The structural union of the columns is preferred, with the bottom of the Distillation zone for the separation of oxygen can be designed as a discharge cup. Through this Measures can reduce the investment costs because the sump pump and the reboiler Distillation zone for the separation of oxygen can be omitted and only one for both distillation zones Column is required.

The top product from the distillation zone upstream of the extractive distillation can be fed to the extractive distillation _{without mixing with other butadiene-containing C 4 hydrocarbon mixtures.} However, before it is fed to the extractive distillation, the top product is expediently fed to a butadiene-containing Q-hydrocarbon mixture which represents the main flow to the extractive distillation. Such as a main stream for the extractive distillation? .U used butadiene-containing C ₄ -Kohlen wasserstoffgernischo be z. B. in the production of ethylene and / or propylene by thermal cracking of a petroleum fraction, z. B. of liquefied. ' Petroleum gas (LPG), mineral spirits (naphtha), gas oil and the like are obtained as a hydrocarbon fraction. Furthermore, such Q fractions are obtained in the catalytic dehydrogenation of η-butane and / or η-butene.

As a selective solvent, for example, carboxamides such as dimethylformamide, diethylformamide, Dimethylacetamide, formylmorpholine, acetonitrile, furfural, N-methylpyrrolidone, butyrolactone, acetone and their mixtures with water. With particular advantage is N-methylpyrrolidone as selective solvent used.

More soluble hydrocarbons in the selective solvent butadiene are, for example, vinyl acetylene, ethyl acetylene and 1,2-butadiene. In the selective solvent Less soluble hydrocarbons than butadiene are, for example, butanes, n-butenes. Isobutene.

The extractive distillation can be carried out using an extractive distillation zone. However, the process for the production of butadiene is particularly advantageous when using two extractive distillation zones connected in series performed using the same selective solvent. Here, for example in the first stage of the extractive distillation one containing the less soluble hydrocarbons Distillate (raffinate) and a butadiene and the more soluble hydrocarbons and the selective solvent obtained extract containing. This extract is freed from the selective solvent, using a mixture of Butadiene and the more soluble hydrocarbons is obtained. This mixture is used in a second subjected extractive distillation zone to a second extractive distillation with the selective solvent, butadiene being obtained as a distillate and an extract containing the more soluble hydrocarbons including the higher acetylenes and remaining butadiene and the selective solvent contains. The extract obtained is then freed from the selective solvent, with a die obtained more soluble hydrocarbons including the Cf-acetylenes containing hydrocarbon stream will.

The butadiene obtained from the extractive distillation is generally used to remove still possibly existing small amounts of propyne and Cs hydrocarbons a downstream Distillation, e.g. B. in one or two distillation columns subjected. The distillative separation of Propyne and Cs hydrocarbons can, however, also be carried out before the extractive distillation.

It can be advantageous to avoid undesirable polymer formation in addition to the Styrene separation from the starting Ct hydrocarbon mixture in the upstream distillation zone in the subsequent extractive distillation in an to add polymerization inhibitors in a known manner. Suitable polymerization inhibitors are, for. B. Furfural, benzaldehyde, aliphatic or aromatic Nitro compounds, hydroquinone, sulfur, sodium nitrite, phenolic compounds such as 4-tert-butylcatechol and aromatic amines such as naphthylamine. This can reduce the tendency of butadiene to polymerize can also be reduced. These inhibitors can also be used in the distillation zone for styrene removal can be used.

F i g. 1 is an embodiment of the method according to the invention. A small amount of oxygen and CU hydrocarbon mixture containing styrene introduced through line 1 into the middle third of the distillation zone 2. At the top of the column 2 is through Line 5 is fed a partial stream of the raffinate to a downstream butadiene recovery plant 9 Vom Bottom of the distillation zone 2 is oxygen-free C. through line 4 in the middle Third of the D'Ssiillatoinszone 3 initiated. On the head the distillation zone 2 is oxygenated C4 carbon) lenhydrogen mixture 13 withdrawn. At the bottom of the distillation zone 3, raffinate is obtained from a downstream one Butadiene recovery plant supplied through line 11. Through line 14 is the sump Distillation zone 3 styrene-containing C «hydrocarbon

Hi mixture of substances with a low butadiene content deducted. At the top of the distillation zone 3 is (via lines 18 and 19) a styrene- and oxygen-free mixture withdrawn, optionally with other C «hydrocarbon mixtures (via line 15) mixed and the

i'i butadiene plant fed through line 12 in which it by extractive distillation using a selective solvent (N-methylpyrrolidone) in a the fraction containing butenes (raffinate) 10. a raw butadiene stream and that containing the (^ -acetylenes) the stream 8 is separated. The raw butadiene stream and the Cj and Cs hydrocarbons it contains and butadiene-1.2 are distilled into the propyne stream 16, the butadiene-1.2 stream 17 and the Pure butadiene stream 7 separated. The one after branching off

.'i of the streams 5 and 11 remaining partial stream of the Raffinate is withdrawn via line 6. Part of the head product of the distillation zone 3 is over Lines 18 and 20 are fed to the bottom of the distillation zone 2.

in distillation zones 2 and 3 can be as structurally separate columns, as indicated in Figure I, or are structurally combined, the bottom of the distillation zone 2 being designed as a drainage cup can (Fig. 2). However, the procedure can also be carried out as in

) "> Fig. 3 shown with two separate, conventionally connected columns, i.e. without recirculation of

Top product from distillation zone 3 in distillatoinszo-

ne 2, be executed.

The example below serves to further

■ "> Explanation of the invention.

example

A C «hydrocarbon mixture of the following The composition is separated in an apparatus according to Fig. 2:

Isobutene

Butene-2-trans

Butene-2-cis

Butadiene-U

Butadiene-1.2

Butyne

Vinyteyclohexene

Styrene

oxygen

Wt%

15.67
75.0

0.2

0.1

2.0

1.0

0.03

450 g / h of this hydrocarbon mixture are via line 1 on the 4th floor from the bottom of the Column upper part 2 with 5 trays introduced. 1.6 g / h of a mixture of 123 are introduced at the top of the column % By weight of oxygen and hydrocarbons are separated off via line 13. The pressure at the top is increased to 4.2 bar held. The liquid bottom product is introduced into the 5th tray of the lower column part 3 with 9 trays A temperature of 42.7 "C. is maintained at the bottom with adjustment of the sump drainage mass. By additional supply (via line 5) of butene at the head ' the distillation to the oxygen separation 2 can

Loss of butadiene in the oxygen-containing overhead product this distillation can be reduced.

At the top of the lower part of the column 3, part of the hydrocarbon vapor is allowed to flow into the upper part from below. Another part is drawn off as a styrene-free product with 0.2 ppm by weight of oxygen (via line 12). When 500 g / h of a butene mixture are introduced at the bottom of the lower part of the column (via line 11), a bottom product with a butadiene content of only 5% is obtained. There. ^c used butene mixture has the following composition:

Wt% Cj hydrocarbons 0.7 butane 13.6 iso-butane 3.4 Butes! 26.5 iso-butene 39.7 Butene-2-trans 8.6 Butene-2-cis 7.2

Butadiene-1.3

Cs- hydrocarbons

Weight o / o
0.2
0.1

In this procedure, the butadiene loss in the bottom product is 0.8%.

If only 150 g / h of the butadiene mixture are added under otherwise identical conditions, the rate increases Loss of butadiene in the bottom product to 4.7%. Without the addition of the butadiene mixture, the butadiene loss is 14.5% in the bottom product, based on the amount of butadiene in the feed.

The styrene-free O-hydrocarbon mixture withdrawn via line 12 is a Q fraction fed in via line 12 from an ethylene plant mixed in, and the resulting C <carbon hydrogen mixture is made by extractive distillation using N-methylenepyrrolidone as the selective solvent separated in the extraction distillation plant 9.

For this purpose 3 sheets of drawings

Claims (8)

Patent claims: J. Process for the production of butadiene with the aid of a selective solvent from a Q-hydrocarbon mixture, which contains butadiene, small amounts of styrene and possibly oxygen, In the selective solvent more soluble hydrocarbons than butadiene and in the selective Lö- ι ο solvent contains fewer soluble hydrocarbons than butadiene, in which the Q-hydrocarbon mixture by extractive distillation into one containing the less soluble hydrocarbons Distillate, a stream of butadiene, and a stream containing the more soluble hydrocarbons is separated, characterized in that that from the Ci hydrocarbon mixture in a distillation zone upstream of the extractive distillation, a mixture of styrene and C «-hydrocarbons is separated, the The bottom temperature of the distillation zone is kept between 40 and 70 ° C, and the top product of the Distillation zone is fed to the extractive distillation 2. The method according to claim 1, characterized in that that the upstream distillation zone at the same time a second stream of liquid or gaseous C3 and / or Ct hydrocarbons is fed. 3. The method according to claim 2, characterized in that the vorgzschall 2s distillation zone as a second current eic saturated or monoolefinically unsaturated C 4 K0; nwasserstoff or a mixture of saturated and / or simply i "> olefinically unsaturated C4 hydrocarbons is fed. 4. The method according to claim 2 and 3, characterized in that the second hydrocarbon stream at or below the inlet point of the -to Styrene-containing Gt hydrocarbon mixture is fed to the further distillation zone. 5. The method of claim 2 to 4, characterized in that the second hydrocarbon stream in the lower third of the further distillation v> zone is supplied. 6. The method according to claim 1 to 5, characterized in that, when oxygen is present in the C4 hydrocarbon mixture containing small amounts of styrene, the C * hydrocarbon mixture is first fed to a distillation zone for the separation of oxygen, in which the oxygen containing overhead and a styrene-containing bottom product are obtained, and thereafter, the styrene-containing sump v> product as a feedstock for the extractive distillation upstream distillation zone is used. 7. The method according to claim 6, characterized in that that part of the top product of the distillation zone upstream of the extractive distillation is fed at the bottom of the distillation zone for the separation of oxygen. 8. The method according to claim 1 to 7, characterized in that the top product from the ''> Extractive distillation upstream distillation zone before feeding to the extractive Distillation of a butadiene-containing Q hydrocarbon mixture is fed, which represents the main stream to the extractive distillation.